Offset rotor vane pump



July 4, 1944.

w. H. cuR'ns OFFSET "ROTOR VANE PUMP Filed March 8, 1939 3 Sheets-Sheet J INVENTOR. Y W/m'a v ATTORNEY.

July 4-, w. cu -r s 2,352,941

OFFSET ROTOR VANE PUMP Filed March 8, 1939 3 Sheets-Sheet 2 1N VENT OR.

BY-D/ZZMM /%fmnm ATTORNEY.

y 1944? w. H. CURTIS 2,352,941

OFFSET ROTOR VANE PUMP Filed March 8, 1939 3 Sheets-Sheet 3 BY l l i/h'am 5. 6200915 ATTORNEY.

Patented July 4, 1944 OFFSET ROTOR- VANE PUMP William H. Curtis, Dayton, Ohio, assignor to Curtis Pump Company, Dayton, Ohio, a corporation of Ohio Application March 8, 1939, Serial No. 260,570

8 Claims.

This-invention relates to vane pumps of the offset rotor type wherein the bore of the cylinder is so formed that the ends of the vanes oscilcharacter having the cylinder bore so formed that th volume of fluid transferred from the low to the high pressure side of the pump will be substantially the same per unit of angular movement at all points of rotation of the shaft, whereby pulsationless discharge will be so nearly achieved as to satisfy most practical purposes.

Another object is to so form the interior curvature of the cylinder of a pump of this kind, that there will be no sharp changes in the oscillatory velocity of the vanes as their ends move over the cylinder wall, to the end that mechanical shock will be absent even at exceptionally high speeds.

In the art as known, substantially pulsationless discharge and mechanical smoothness have not been achieved in-one and the same structure, due to the fact that attainment of the one imposes conditions which make it highly difiicult to fulfill the other.

It is therefore another object of this invention to so design a pump of this type that mechanical and hydraulic smoothness are each substantially present, each without sacrificing the other.

Another object is to so form the cylinder bore curvature that the radius of curvature at any point is as near the rotor axis as possible whereby the pressure angle of the bore with the end of the blade will be kept at a minimum.

Another object is to so form and proportion the several curves comprising the cylinder bore,

a rotary pump of the character hereinbefore dis cussed and having a cylinder bore curvature made upof two oppositecircle arcs having their ends joined by opposite curves which take the form of an Archimedes spiral. The pump of 1 is no part of this invention and is shown only for comparison with the improved pump herein disclosed.

Fig. 2 is an outline of the cylinder bore which may be employed in the pump of Fig. 1, and which produces, when so employed a theoretical non pulsating delivery, but with the disadvantage that there is such pronounced mechanical shock that the device is wholly impracticable.

Fig. 3 shows a pair of circle arcs of diiferent radii having common tangents at their point of juncture.

Fig. 4 shows the upper left quadrant of the bore of Fig. 2' to an enlarged scale together with a corrective curve which should replace the middle portion of the original curve of the quadran if mechanical shock is to be eliminated.

Fig. 5 shows the complete outline of a cylinder bore which is employed in the pump of Fig. 6 and which has the corrective curve shown in Fig. 4 applied thereto, whereby substantially non pulsating delivery is achieved and mechanical shock prevented.

Fig. 6 is an axially-transverse section through a pump with the cylinder bore of Fig. 5 embodied, the section being taken at 6-6 of Fi 7.

Fig. 7 is an axial section taken at '|--'l of Fig. 6 through the improved pump structure.

Fig. 8 is a side view of one of the vanes employed in the pump of Figs. 6 and 7.

Fig. 9 shows a vane with sealing members at the ends and for which, when employed, proper allowance must be made in the cylinder bore.

Figs. 10 to 13 show the manner of laying out the cylinder bore for several types of vane ends.

Referring now to Fig. 1; the body I l of a rotary pump has a cylinder bore l2 against the upper side M of which the rotor i6 has bearing. The rotor i6 is rotatable on shaft i8 which has hear-- ing in the hub 20.

The rotor I6 is provided with slots 22 at right angles to each other and with vanes 24 and 26 which are slidable radially in these slots. The vanes 24 and 26 are cut away at 28 to clear each other, the cut away portion being sufficient to permit th maximum radial movement of the vanes without interference with each other.

The vanes 24 and 26 are longer than the rotor diameter and consequently project radially beyond the rotor at one or the other end, the cylinder bore I! being of such contour that the tion of the vane part 38 must also be cc vanes may be rotated therein by sliding back and forth in the rotor slots. For convenience in description, the centerlines of the vanes are designated by letters CC: and C103.

Interchangeable suction and discharge ports 21 and 29 are provided in the form of slots each extending circumferentialy over. one blade span and preferably having an axial width considerably less than the axialmeasurement of the rotor.

Since both ends of a vane must contact the cylinder bore at all points of rotation of the rotor, obviously the bore I! may not. be round, since CC'2=C1C3=AG=BF. The bore in fact comprises a sealing zone are CACi having the radius A0 of the rotor, a diametrically opposite pumping zone arc CzGCa having aradius 0G equal to the rotor radius plus .the excess of the vane length any point of its rotation. The sealing and pumping zone arcs both have their center at O, the axis of the rotor.

Now since the fluid occupying the space 30 is bounded by two circle arcs having the same center, it follows that uniform rotation of a vane from C3 to C2 effects a uniform delivery of the fluid within the space 30 into the space 32, so that, if there are no other unbalancing effects, non pulsating delivery is fully achieved. It must be noted, however, that while one vane is passing from C; to C2. another is passing from C: to C1. The explanation of how this afiects the volume in the space 3! follows.

'If a vane could move fromJCr to 01 without retracting into the rotor, the volume in space 32 would be neither increased nor decreased by such movement. 'I'hefact is, however, that while a vane passes from C: to C1, the extended blade portion 38 which projects from the rotor at C: retracts wholly into the rotor slot, thereby removing just that much metal out of space 32 which must be replaced by a volume of liquid equal to the volume of-metal removed. It follows that the volume of fluid delivered from the discharge end ll per' quarterturn of the rotor is equal to the volume in the space 30 minus the volume of the part 36 of a blade. It has been shown by reference to Fig. 1 that movement of a fluid from space ll to space 32 is constant when the rotor speed is constant, that is, if any one degree of rotor rotation transfers a given volume of fluid from the space 30 to the space 32, then every other degree of the ninety degrees rotation between C: and C:

will transfer an equal volume.

It follows that, if the ultimate discharge from the end 32 is to be constant, the rate of r tractant, that'is, any degree of rotation of the ninety degrees from C: to C1, must reduce the volume of the extended portion of a vane the same amount as any other degree.

To illustrate still further by a concrete example, suppose that each degree of rotation in the directionof the arrow 38 will cause the vane 24, by moving anti-clockwise away from Ca, to transfer one cubic inch of liquid from the space It a into the space 32, and that upon each degree of movement of the vane 28 from C: toward C1 the volume of the blade portion remaining extended vwill have been decreased by one tenth cubic inch,

then the discharge at 34 will 'be exactly nine" 4 tenths cubic inch for each and every degree of rotationbf the rotor. The discharge rate will then be theoretically constant and pulsationless' discharge will be attained. t

.Now to satisfy the foregoing conditions mechanically the cylinder bore of the four vane pump shown in Fig. 1 must have a cross sectional contour such as is shown in Fig. 2. In this bore the arc CCl is drawn with the radius of the rotor,

tation as in any other degree. The polar equa-.

tion ,of the Archimedes spiral is r=a0+c, wherein r=polar ordinate, c=a constant, 0=angular distance in radians of r from; the initial line, and c=a constant. The constants a and c are so selected as to cause the curve to pass through 0 and B as in Fig. 4, the lengths, and locations of 0C and OB-having been previously ascertained from the required proportions of the particular pump under consideration.

With a bore such as is shown in Fig. 2 incorporated. in the pump Fig. 1, and assuming a constant velocity of rotation, the velocity of retraction of the part 36 of a vane is exactly the same per unit of rotation throughout its movement from C2 to C1. In such a pump, however, a vane, after moving from C3 to 0: without retraction,

instantly changes at C: from zero rate of retraction to the maximum rate of retraction, and then with uniform angular velocity of the rotor, t, or time, may be substitutedqior 0 whereby %=a=velocity of vane (retraction or extension) assertion %=0= acceleration of vane (retraction or extension) proving that there isno acceleration of the vane A along the path of thecurve CB. All of it must' therefore have been acquired at the entrance to, or. exitfrom, the curve.

Now it is axiomatic that unless the several curves making up the cross sectional contour of the cylinder bore of a pump of this character have common tangents at their points of Juneture, practical operation is impossible. Thecurve of Fig. 3, for instance, comprises two circle arcs an and sm'the first with center 0 and radius 0W and the second with center 01 and radius O1W1. Obviously the tangent TI'i is common to both curves, and obviously a vane such as is shown in-Fig. 1 sail or II would pass from one to the other of these curves without mechan;

ical shock."

In order to further illustrate the impracticability of a pump bore such as is shown in Fig. 2, the locations of tangents to the arcs and curves at their points of juncture are computed and indicated as shown thereon to prove that, in such a bore, common tangents do not exist. Referring to Fig. 2, the line M01 is the tangent to the arc CA'C1 at the point C]. and NCr is the tangent to the curve C1FC2 at the same point. Also PCz is the tangent to the arc GaGCz at the point C: and RC2 is the tangent to the curve CIFCZ at the same point. It is clear that there are no tangents in common. It can be shown mathematically that it is impossible to develop an Archimedes spiral tangent to a circle are where the pole of'spiral is at the same point as the center of the arc, as it must be in this construction. To illustrate mathematically:

If is the angle between the tangent and the polar ordinate, then Q if it is common with the tangent to the circle are at the same point. But, for the curve of the Archimedes spiral heretofore given as r=a+c. 9 at point C (inasmuch as 00 is the initial line for the curve CB) equals zero, and 1:0. Also d7 al d9 equ s a Therefore C tan (lbequals a finite value less than infinity. Therefore the curve cannot be made tangent to the circle arc. The Archimedes spiral, notwithstanding the uniform delivery which would accrue from its use cannot be employed without some modification or correction at the points C, C1, C2, and C3.

In my copending application Serial No. 204,- 108, filed April 25, 1938, now Patent No. 2,165,963, issued July 11, 1939, substantially the same illustrative discussion was employed as is herein presented, to show that the pump cylinder bore herein shown in Fig. 2, comprising two opposite circle arcs of equal angle and different radius, having their ends joined by curves of equal radial increase per unvarying increment of rotation, as in an Archimedes spiral, would provide a pump having a theoretically uniform discharge, but could not be practically employed because common tangents do not exist at the juncture points between the several curves comprising the bore.

In the copending application, supra, the pump herein shown as Fig. 1 with a bore as in Fig. 2, was explained, then dismissed as too impractical for further consideration, since no way was then known to modify the bore to adapt it to practical'use.

However, a way has now been found whereby a bore of the class described may be modified by the introduction of a corrective curve of another order between the ends of the Archimedes spirals and the circle arcs of the bore, so that while theoretically pulsationless discharge will not be wholly attained, the approach to it is so close as to satisfy most practical requirements.

Fig. 4 is an enlarged view of a quadrant, as

A03, Fig. 1, but with the introduction of another curve DE for correcting the defect at C. The most desirable form for this correcting curve is one that will impart constant acceleration throughout its length to a vane, as the vane passes over it. (Acceleration is here spoken of in its algebraic sense, that is, it may be either plus or minus depending on the direction of rotation.) For, if the acceleration is constant throughout the length of this correcting curve, it will obviously have a minimum value, and the forces acting upon the vane will thereby be greatly reduced. The curve required to meet this situation is a parabolic spiral which for convenience may have the form,

which has for its first derivative and for its second derivative (c is a constant equal to A0 in all. equations. 0 equals radians between positionof r in the curve EB and its initial line 0C. And 01 equals radians between n in the curve DE and its initial line OD.)

The boundary conditions for this correcting curve require that its polar ordinate equal OD 'at D and OE at E. Also that it be tangent to the circle arc at D and to the curve EB at E. It.

is inherently tangent to the circle are at D for,

as 01 equals zero at this point.

' Now tan at E on the curve a6+c EB a da and tan at E on the curve i 1 1 6 d 7] 2(1 61 d6,

therefore to meet the boundary conditions a,0 +c a0+c 2am must equal Having selected its length in terms of radians, 0 and 01 are automatically evaluated, and the value of the constant m can likewise be determined. v l

To summarize for Fig. 4.

AD is a circle arc with radius CA. I

DE is a parabolic spiral with initial line 01) and 5 equation r1=a101 +c.

EB is an Archimedes spiral with initial line C and equation r=a0+c..

OB is one half the vane length.

OB minus 0A represents one half themaxll0 mum blade extension as measured from the I rotor. a 4 Fig. 5 shows the outline of a complete bore formed in accordance with the foregoing calculations. The ordinates ior the quadrant A03 only need be calculated. Quadrant GOF is then determined by extending these ordinates through 0 and laying out, or measuring thereon, a constant distance AG from the curve ADEB. In other words, if 1 equals the opposite ordinate for go curve GDIEIF, and L equals the vane length, y=L--r or y=L r1. The quadrant AOF is then laid out as a symmetrical reproduction of A03, and the quadrant BOG a symmetrical reproduction of FOG. 7

Figs. 6 and 7 show a complete pump the body of which has a bore 39 of the outline shown in Fig. 5.

. 'I'hispump comprises a body 40 counterbored to receive the end closing head 42 which is held to the body by the screws 44. Hub 46 provides rotative bearing for the rotor shaft 48. E g

The rotor which may be broadly designated by the numeral 50, comprisesa disc 52 at the inner I end of shaft 48 and a ring-of larger diameter than the disc extending from the disc. The ring has a large central opening 53 extending all the way through the ring to the disc. Thering is cut through 'to the disc by two radial slots 54 extending at right angles to each other, whereby the remainder of the ring comprises four equal segmental lugs 56.

Two throughvanes 58 are slidably fitted to the slots 54, the vanes being'notched half way through at their middle as at 80 (see' Fig. 8)

the notches being of such length as will prevent 5 interference 'of the vanes, .one with the other, as they slide back and forth through the slots. 5 The end of the vanes have arcuate grooves 62 into which the seal bars 84 are rockably fitted. Fig. 11 shows the end of a vane 58 to an enlarged scale. Here the cylinder bore curve CiEB passes exactlygthrough the center of the radius T3 of the rocker seal bar 4. The measurement between the centers of opposite rocker seal bars in the same vane is therefore AG=BF, the vane operating in this case exactly like a theoretical vane having zero thickness and a length BF. The cylinder bore Figs. 4 and 5 is therefore laid .out for such a theoretical vane.

Interchangeable suction and discharge ports 66 and 168 are provided in the form of circum-' ferentially extending slots having an axially extending width considerably less than the axial' measurement of the rotor body (see Fig. 7), so as to leave ample bearing for the ends of the vanes as they pass over the ports. Rotation of the pump may be in either direction, but for purposes of description rotation may be in the direction of the arrow ll. This will make the space 12 the low pressure side and the space I4 70 the high pressure side of the pump.

The are -DAD2, with which the rotor is in constant contact, comprises a sealing zone, while the arc DIGDJ, having its center in the rotor axis,

plus CUIVBS C6D1 and DaC1 comprise the pumping tangents at their points of juncture.

It will also be recalled that the bore 39, Fig.

zone. It should be noted that the sealing zone are extends over less than a blade span by an amount equal to the corrective curve portions D04 and DaCs while the pumping zone extends over an entire blade span. The volume pumped per quarter revolution of the rotor will therefore be the volume in-the space 15 between two rotor blades, minus the volume of blade extension at C5.

- The shortening of the sealing zone is necessary for the reason that, with the bore shown,

the blade is not fully retracted in the rotor at Ce but must continue on to D2 before full retraction has been effected. If the port ended at C0, and rotation was in the direction of'the arrow I0, the fluid in the small space 14 between the rotor body and the cylinder bore 39 would be trapped and forced through the sealing zone.

- Such a condition would result in a decided shock and must therefore be avoided.

It will be recalled that the pump of Fig. 1, wherein the bore l2 comprises two circle arcs joined by Archimedes spirals, was shown to have theoretically uniform discharge, because. every unit of rotation; of a vane through the pumping .zonemoved an equal volume of liquid, and every like unit of rotation of a blade over the discharge port retracted an equal volume of the blade ex? tension into the rotor, but that this pump was mechanically impracticable because the several curves comprising the bore I2 had not common 5, incorporatedin the pump of Figs. 6 and 7, is

.made up of two opposite circle arcs, two opposite Archimedes spirals midway of the circle' arcs, and four parabolic spirals connecting the respective ends of the circle arcs and Archimedes spirals, and .that common tangents exist at the juncture of all of the curves of the bore.

Obviously substantial theoretical perfection is attained mechanically in the movement of the vanes 54 around the bore 39, and perfection is so nearly attained hydraulically as to meet most reasonable requirements, for instance, while a vane rotates uniformly from D: to D1 over the .circle arc portion of the pumping zone thereby transferring uniform volumes per unit of rotation from space I5 into space "14, another vane moves from E1 to E2 over the Archimedes spiral portion of the discharge zone thereby retracting an equal proportion of the total blade retraction per unit of. rotation.

In the instant case, although not necessarily.

always, the circle arc portion DrGD: extends over two thildSoOf the pumping zone, while the Archimedes spiral portion extends over a corresponding two thirds of the discharge zone.

-In this two thirds of each quarter revolution,

unit of rotation. Similarly from Cs to E1 there, is a slight acceleration of blade retraction and .from E: to Co slight deceleration of blade retraction. These slight deviations from uniformity are too small to be noticeable at conventional speeds.

. Among the objects of the. invention enumerated is the maintaining of a minimum pressure angle between vanes and bore surface. This pressure angle is the complement of the angle between the center line of the vane and the tangent to the curve at the point of vane contact.

It is desirable to hold this pressure angle to as low a value as possible to prevent excessive thrust components being built up between vane, rotor slot and bore surface, acondition which would cause excessive wear.

Treating a vane as having no thickness, the tangent of this pressure angle is equal to the cotangent of which equals Following out this calculation it may be shown that the greatest pressure angle will fall at E. Obviously the pressure angle may be made less as the difierence between the sealing zone radius and the pumping zone radius is made less. The amount of their difierence determines the capacity of a pump of a given size, the greater the difference the greater the capacity.

It has been shown by reference to Figs. 6 and 11 that vane ends could be provided with rocker seal bars so made that a cylinder bore, Fig. 5,

to be used therewith could be calculated for a vane of zero thickness and length BF. Fig. shows a similar but less approved method of treating the vane end'to achieve a similar result.

In Fig. 10, a vane 59a is shown in the bore 39, Fig. 5, at E2. If this vane is revolved 180 degrees to E3 the curve of the bore will be angled with respect to the vane as at 39a. The vane will have an actual length of E2E3, Fig. 6, that is, the same as the length of a theoretical vane of zero thickness and length BF, and will operate in the bore of Fig. 5.

The vane end, Fig. 10, is somewhat objectionable in that at E2 the vane comes to a point 6!. When this vane rotates in the bore of Fig. 5, while it is passing from D2 to D1, bearing of the vane end against the cylinder wall will be along the surface 63 and while it is passing from D3 to D, the bearing will be along the surface 55, but while it is passing 'over the sealing and pumping zones, the point 6| only of the vane will bear on the cylinder wall. During this time, that the point 61 only bears on the cylinder wall, the vaneis not being forced to retract into the rotor slot by pressure against the vane end.

The arrangement of Fig. 10, while it provides one means of avoiding the use of rocker seal bars on the vane ends, is not approved,

' since a better way to accomplish this result may be had by the arrangement shown in Fig. 12.

In Fig. 12, a radius T is selected for the vane end whichv will leave the corner 6.? well away from contact with a cylinder bore 69 when the vane end is passing over that part of the bore having the A theogiven for plotting the bore 39, Fig. 5, this theoretical bore'passing through the point 0. The actual bore 69. is then determined by having the minimum distance from any point on the curve 39b to the curve 69 equal to T4.

When it is desired that maximum capacity for a given size pump be attained, and the difference between the sealing zone radius and the pumping zone radius is accordingly made considerable, and relatively high blade pressure angle results, the ends H Fig. 11, of the blade may be cut away to such an extent as to leave insull'icient depth to the groove 62 to adequately support the rocker seal bar 64. I

In such a case, the method illustrated in Figs. 9 and 13 should be followed. Here a theoretical bore 39c, Fig. 13, is plotted to extend through the center K of the bar from which the rocker seal is I made. This theoretical curve is developed from the equation-given for the bore 39, Fig. 5. A uniform minimum distance I3 is then maintained between the theoretical bore 39c and the actual bore 11. This same dimension I3 is added to a bar 64, Fig. 11, to provide the bar 18, Fig. 13, the outer surface of the bar at Bil being formed to the minimum radius of curvature of the bore. It will be seen that the rocker 18, Fig. 13, has more bearing in the end of the vane than the rocker 64, Fig. 11.

The improved bore 39, Fig. 5, is shown only as applied to a through vane pump, that is, two connected vanes in one rotor slot, and with slots 1 spaced at right angles, but it will be understood that the bore may be applied with almost equal advantage to rotary pumps having a difierent number of rotor slots, or divided vanes, that is, two vanes per slot, either with the usual spring means for urging pairs of vanes in the same slot outwardly into contact with the. bore, or otherwise kept against the bore.

In the embodiment shown, the pump body itself is bored to the improved outline 39, but obviously the pump body or casing may be provided with a separate cylinder, or liner having its inner periphery formed to the outline shown.

While one embodiment of the invention only is Herein shown and described, it is obvious that considerable alteration in structure may be made without departing from the spirit of the invention as defined in the appended claims.

I claim:

1. In a pump of the offset rotor type, a cylinder having a bore, the cross section of which, taken at right angles to the axis is composed of one circle are drawn from the rotor axis to a radius equal to the rotor radius, a second circle are opposite the first drawn from the rotor axis to a larger radius, two pposite Archimedes spirals intermediate these said arcs, and four parabolic curves joining the ends of the arcs to the ends of the Archimedes spirals, the arcs and curves being so formed and arranged that there are common tangents at all points of juncture.

2. In an offset rotor sliding multiple vane pump, a cylinder having a bore, the normal cross sectional contour of which comprises a circle are drawn from the axis of the rotor with a radius equal to that of the rotor, an opposite circle arc drawn also from the rotor axis but with larger radius, two opposite Archimedes spirals intermediate the said arcs, and four parabolic spirals joining the ends of the arcs to, the. ends of the Archimedes spirals, said arcs and curves all having common tangents at their points of juncture, the respective lengths of the arcs and curves being such that a given point of one, parabolic spiral is spaced from the corresponding point of the next parabolic spiral a distance equal to one or more whole. vane spans.

3. In an offset rotor sliding vane pump, a cylinder having a bore, the cross sectional outline of which comprises a circle are drawn from the rotor axis with a radius equal to that of the rotor. an opposite circle are drawn also from the rotor axis but of larger radius, two opposite spirals of uni form retraction intermediate the said arcs, and

four curves of uniform acceleration Joining the ends of the arcs to the ends of the curves of uni form-retraction, said arcs and curves all having common tangents at their points of juncture, said cylinder having opposite suction and discharge ports each of which extends from an end of the first circle newer one of. the curves of uniformacceleration, over one of the curves of uniform retraction and half way over the next curve of uniform acceleration.

4. In a pump ofthe offset rotor sliding vane typ a pump body having a somewhat cylindrical bore, a cross section of which, taken in a plane normal to the axis, is defined by two opposite concentric arcs of unequal radii, with vane extendend portions comprising curves of uniform ac-, 25 celeration, the several curves and arcs all having common tangents at their points of juncture.

5. In a pump of the offset rotor sliding multiple vane type, a pump body having a somewhat cylindrical bore, a cross section of which, taken in a plane normal to the axis, is defined by two opposite concentric arcs of unequal radii, with vane extending and retracting curves Joining the ends of the arcs, a cylindrical rotor having a diameter of twice the smaller of the two radii rotatably positioned with its axis at the center of the arcs, said rotor having radial vane slots, vanes slidable in said slots, the ends of the vanes being always in contact with said bore, the vane extending and retracting curves having a middle portion so formed as to provide uniform extension or retraction of a vane per unit of rotation and two end portions so formed as to provide uniform acceleration or deceleration to a vane per unit of rotation,'the several curves and arcs all having common tangents at their points of juncture.

6. The structure defined in claim 5 wherein suction and discharge ports extend from an end of the smaller are over one of the portions which provide uniform acceleration or deceleration, over the portion which provides uniform extension or retraction and half way over the other portion which provides uniform acceleration or' generated along parabolic spirals and joining the ends of said cylindrical surfaces to the ends of said first two intermediate curved surfaces, there being common tangents at the points of juncture of all of said cylindrical and curved surfaces.

8. In a rotary fluid handling device including a slotted oflset rotor having a plurality of vanes radially slidable in said slots, a housing for said rotor having a bore of improved construction, said bore being provided with two oppositely disposed cylindrical surfaces having a common axis but unequal radii, two oppositely disposed curved surfaces intermediate but not joining said cylindrical surfaces, each of said. curved surfaces being generated along an Archimedes spiral, and four other curved surfaces generated along parabolic spirals and Joining the ends of saldcylin drlcal surfaces to the ends of said first two intermediate curved surfaces, there being common tangents at the points of juncture of all of said cylindrical and curved surfaces.

WILLIAM H. CURTIS. 

